The present invention concerns a module for filtering, separating, purifying gases or liquids, or for catalytic conversion, comprising within a housing at least one rigid treatment element for purification or having a membrane for separating, filtering, or catalytic conversion. Such a module may be used for filtering, separating or purifying liquids but it is especially applicable to filtering or purifying gases used for example in the manufacture of semiconductors.
This type of module comprises:
- a generally cylindrical metal envelope or housing, comprising one part or a plurality of parts assembled by fused metal bonding;
- one or more rigid treatment elements, of tubular shape or of multi-channel type, such as is described in U.S. Pat. No. 4,069,157, or of honeycomb type, such as is described in U.S. Pat. No. 4,781,831;
In applications for filtering or purifying gases to be used especially for the manufacture of semiconductors, the module assembly must be able to withstand:
- thermal stresses arising from use (thermal cycling and degassing for example),
- mechanical stresses in withstanding pressure, such as for example in treating a gas which can be at several hundreds of bars,
- corrosion by the treated fluid, which may be for example HCl, a chloride, a bromide or another corrosive gas used in producing integrated circuits, especially in etching.
Moreover the requirements for ultra-cleanliness in the electronics industry require that there shall be no risk of polluting particles being thrown out by the module.
Such a module should be capable of functioning at temperatures going from ambient temperature to several hundreds of degrees Celsius, whether for treating the fluid or for cleaning or regeneration of the treatment element or elements. Differences in expansion appear between the element and the housing with the effects of variations in temperature and can amount to several millimeters when the treatment element has a length in the order of a meter. The element-to-housing connection has to be sufficiently flexible to be able to deform in such a way as to compensate for these differences in expansion.
In some known assemblies, the element-to-housing connection can be effected by way of a polymer or elastomer gasket, for example of PTFE, EPDM, a silicone, etc. In this case the elasticity of the gasket is used to compensate for the differences in expansion between the element and the housing.
This solution is not suitable for high temperature uses, for the obvious reasons of physical-chemical and mechanical degradation of the polymer or elastomer. Moreover these materials age and creep with time.
Modules are also known in which the connection of the element or elements to the housing is effected through one or more metal parts or rings located at the ends of the element. Each of these parts is fixed securely both to the metal envelope and also to the end of a treatment element, by brazing or by glass (or enamel). These solutions suffer from major problems.
Firstly, brazing does not usually provide good corrosion resistance with gases such as HCl, chlorides, bromides, etc., which are used at present for etching integrated circuits.
Secondly, glasses which have good corrosion resistance are in general terms those which do not comprise components in their composition which fuse at a low temperature. These glasses thus melt at high temperatures. Assembly of the module by means of these glasses requires the module assembly to be raised to a high temperature, which is not always possible because of the risk of damaging the treatment element (filter layer, catalyst, etc.), or the metal of the ring. Moreover, in order to obtain a good bond between the glass and the metal of the housing or of the ring, it is generally necessary firstly to oxidize the metal surface, which is incompatible with the ultra-cleanliness imposed in applications to the manufacture of semiconductors for example. Finally, this glass solution is costly, because it involves large heating means and a method that is complex.